The signature machine addressed by the present invention is generally well known. An extracting cylinder rotates adjacent a hopper in which signatures are stacked The signature next to be fed to the gatherer is extracted from the hopper by a clamp of one form or another and the clamped signature is carried by the extracting cylinder to a stop or register gauge. Here, the signature is released so that it may be opened by spreading the leaves or sheets of the signature
There may be as many as twenty or thirty hoppers, each with its own extracting cylinder. The extracting cylinder is sometimes called a drum, but regardless of the name it is usually a pair of rotating discs keyed to a driven shaft.
Opening of the signature is accomplished by two smaller cylinders positioned beneath the extracting cylinder. One cylinder is generally known as the opening cylinder, and the other cylinder is usually termed the lap cylinder. These two cylinders are also equipped with clamps effective to clamp the free edges of the respective legs or sheets of the signature. The cylinders rotate in opposed directions so that the clamps are effective to open or spread the signature, eventually dropping it on to the gatherer.
The signature is folded unevenly so that there is a short sheet and a long sheet. The long sheet is distinguished by its so-called lap margin, this being the portion of the free edge which is longer than the short sheet. The extended or longer margin plays an important role in effectively opening the signature and assuring rapid, continuous operation.
Dependable operation at high speed, without jamming, involves assurance the clamp on the lap cylinder will effectively clamp the lap margin. This is not only a delicate matter of proper timing, it also involves the inertia characteristics of the paper signature at the time it has been released by the extracting cylinder, ready to be opened by the clamps on the lap cylinder and the opening cylinder.
To assure dependable operation from the standpoint of effectively clamping the lap margin by the clamp on the lap cylinder, it has been proposed to employ a pair of reciprocating fingers (see U.S. Pat. No. 2,413,358, Kleineberg) intended to support the free edges of the signature at the phase of the cycle where the clamp on the lap cylinder is to become effective. Afterwards, these fingers are withdrawn. The actual mode of operation of the positioning fingers may be widely varied, but in any event there are linear motions which introduce vibration, the mechanism requires a great deal of space which limits the number of signatures which can be fed in a cycle of operation, and the fingers must be positioned outside the extracting cylinder, which s to say neither finger can be located between the rotating discs which define the extracting cylinder.